Ouroboros is a Proof-of-Stake (PoS) consensus mechanism where the consensus is created by:

staking coins in the user's own node by keeping his or her computer online

or by delegating their staking rights to a stakepool. The user does not need to be online.

It uses a game theory-based incentive scheme that incentivizes both nodes and users to keep the system decentralized. The biggest underlying assumption is that there is an honest majority of participants. Time will tell if this assumption holds.

IELE is a virtual machine developed by the Cardano community to run smart contracts. Because of a method called Semantics Based Compilation, developers should be able to write smart contracts on Cardano in any programming language.

Cardano wants to use a governance system where a certain percentage of the consensus rewards are set aside in a treasury, and periodical on-chain voting determines what it is spent on. Stakeholders are asked to vote which funding proposal(s) should receive funding - stakeholder can choose to either directly participate by voting, or to delegate their rights to someone else (e.g., someone trustworthy or more knowledgeable). Voting takes place privately, obscured by zero-knowledge proofs.